The long-term goal of this project is to elucidate the molecular basis of the pathogenic process in transmissible spongiform encephalopathies, a group of neurodegenerative diseases that afflict humans and animals. It is believed that the infectious pathogen is a misfolded form of the prion protein, PrP, which self propagates by binding to normal prion protein and catalyzing its conversion to the pathogenic form. The first specific aim for the next funding period is to gain insight into the conformational and biophysical basis of the amino acid sequence and strain dependent barriers in prion propagation. These studies will be performed using the recently developed in vitro model of nucleated conformational conversion of a disease-associated prion protein variant PrP23-144. The second specific aim is to elucidate alternative pathways and mechanisms of conformational conversion of the recombinant prion protein PrP90-231. We will also determine the effect of selected disease-associated mutations on these conversion pathways, and explore the possibility of using recombinant PrP90-231 as a model for studying the molecular basis of barriers in prion propagation. The final specific aim is to determine the effect of a mutation that stabilizes the normal form of human prion protein on the susceptibility of humanized transgenic mice to infection with the prion agent, and on biophysical properties of human prion protein in vitro. Recently, we have created lines of transgenic mice that express the 'superstable'human PrP variant. We will inoculate these animals with the prion agent from CJD cases, hypothesizing that they should be more resistant to infection than mice expressing the wild-type human PrP. We will also determine the biophysical and structural basis of the remarkably high stability of this prion protein variant. This interdisciplinary project will employ a variety of experimental approaches, ranging from biophysical techniques (FTIR, CD and fluorescence spectroscopy, hydrogen exchange, fiber x-ray diffraction, NMR, spin labeling) to transgenic animal studies.